What if I want label on other side of vertex or fermion?
\begin{center}
\begin{fmffile}{elecdig}
\begin{fmfgraph*}(150,100)
\fmfpen{thin}
\fmfleft{i1,i2,ip,i3,i4}
\fmfright{o1,o2,op,o3,o4}
\fmfpen{thick}
\fmf{fermion,tension=1,label=$v$}{i3,o3}
\fmf{fermion,tension=1,label=Spin Direction}{i4,o4}
%\fmf{fermion,tension=1,label=$spin=+\frac{1}{2}$}{v2,o2}
\fmf{dashes,label=It can't be ${\hat{e}_R}$ but it is $e_R$}{ip,op}
\fmf{phantom,tension=1}{o2,o1}
\fmf{phantom,tension=1}{i2,i1}
\fmf{fermion,tension=1,label=$v_{new}$}{o2,i2}
\fmf{fermion,tension=1,label=Spin Direction}{i1,o1}
%\fmf{fermion,tension=1,label=$spin=+\frac{1}{2}$}{v1,o1}
\fmflabel{Frame $1$.}{i3}
\fmflabel{Frame $2$.}{i2}
\end{fmfgraph*}
\end{fmffile}
\end{center}
I want to move v_new to another side
There is also a problem when I am not using \fmfpen{thick or thin} and the second line from above automatically thin compare to others.
i.e.,
\begin{center}
\begin{fmffile}{elecdig}
\begin{fmfgraph*}(150,100)
%\fmfpen{thin}
\fmfleft{i1,i2,ip,i3,i4}
\fmfright{o1,o2,op,o3,o4}
%\fmfpen{thick}
\fmf{fermion,tension=1,label=$v$}{i3,o3}
\fmf{fermion,tension=1,label=Spin Direction}{i4,o4}
%\fmf{fermion,tension=1,label=$spin=+\frac{1}{2}$}{v2,o2}
\fmf{dashes,label=It can't be ${\hat{e}_R}$ but it is $e_R$}{ip,op}
\fmf{phantom,tension=1}{o2,o1}
\fmf{phantom,tension=1}{i2,i1}
\fmf{fermion,tension=1,label=$v_{new}$}{o2,i2}
\fmf{fermion,tension=1,label=Spin Direction}{i1,o1}
%\fmf{fermion,tension=1,label=$spin=+\frac{1}{2}$}{v1,o1}
\fmflabel{Frame $1$.}{i3}
\fmflabel{Frame $2$.}{i2}
\end{fmfgraph*}
\end{fmffile}
\end{center}
this gives,
I am restating the problem with reference to this image:
-
2nd line from above is thin compare to others
-
I don't know how to shift label $v_{new}$ to other side.
Best Answer
Here's an alternative answer that doesn't use
feynmf
, but uses a new package called TikZ-Feynman (CTAN). TikZ-Feynman has inbuilt support for momentum arrows which, in this case, can be used to indicate the velocity and spin direction of fermions: